The present invention relates to a valve timing control apparatus for variably controlling an opening and closing timing of an intake valve and/or an exhaust valve of an internal combustion engine in accordance with an operating condition of the engine.
A valve timing control apparatus of this kind is adapted to control the opening and closing timing of an engine valve through control of a relative phase between a crankshaft and a camshaft. That is, the apparatus of this kind includes a driving rotary member drivingly connected by way of a timing chain or the like to the crankshaft and rotatable relative to a driven rotary member on the camshaft side. Between the driving and driven rotary members is interposed a phase control mechanism for variably controlling the relative phase therebetween.
There have been developed various phase control mechanisms such as one that uses a helical gear for converting axial motion of a hydraulic piston to rotational motions of the rotary members. Recently, it has been proposed a phase control mechanism of the kind that uses links and has many advantages such as a reduced axial length and a smaller friction loss.
A valve timing control apparatus having a phase control mechanism using links is encountered by a problem that it has a difficulty in obtaining desired performance characteristics since it utilizes a spiral guide of an Archimedes spiral.
It is an object of the present invention to provide a valve timing control apparatus for an internal combustion engine that can make higher the design freedom of links and other parts that are engaged with a spiral guide and can improve the performance characteristics that are related to the spiral of the spiral guide.
To achieve the above object, the present invention provides a valve timing control apparatus for an internal combustion engine comprising a driving rotary member drivingly connected to a crankshaft, a driven rotary member drivingly connected to a camshaft, a plurality of radial guides provided to one of the driving rotary member and the driven rotary member, an intermediate rotary member rotatable relative to the driving rotary member and the driven rotary member and having at a side thereof a spiral guide of a single spiral, a plurality of guided members movably engaged with the respective radial guides and the spiral guide, a plurality of links connecting between the other of the driving rotary member and the driven rotary member and the respective guided members, a control force applying unit for applying to the intermediate rotary member a control force for rotating the intermediate rotary member to rotate relative to the driving rotary member and the driven rotary member, wherein rotation of the intermediate rotary member caused by the control force applying unit causes radial movement of the guided members which is in turn converted to relative rotation between the driving rotary member and the driven rotary member by the links, and wherein the spiral of the spiral guide is defined so that a variation rate of spiral radius per angle is not constant.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.